The invention relates to a circuit arrangement for rectifying the output voltage of a sensor supplied from an oscillator for a non-electrical variable, whose amplitude and phase angle is a measure of the non-electrical variable.
Circuit arrangements such as this form, together with a sensor and an oscillator, which supplies current to the sensor, a measuring device which converts a non-electrical variable, for example a movement distance or a pressure, to an electrical variable, in particular to an electrical voltage, which is a measure of the non-electrical variable. The oscillator supplies the sensor with an AC voltage having a constant frequency and amplitude. The non-electrical variable influences the transmission behavior of the sensor. The amplitude and the phase angle of the output voltage are therefore a measure of the non-electrical variable to be measured. The sensor may be, for example, an inductively or capacitively operating movement sensor, whose transmission behavior can be altered by the deflection of a coupling element. The output voltage of the sensor, which is present in the form of a modulated AC voltage, is converted to a DC voltage for further processing. The AC voltage which is modulated corresponding to the deflection of the coupling element is in this case converted such that the mathematical sign and the level of the DC voltage are a measure of the position of the coupling element. The output voltage of the sensor is made up of the carrier signal, which is referred to below as the useful signal and is modulated corresponding to the deflection of the coupling element, and of interference signals which are superimposed on this carrier signal. The interference signals are picked up, in particular, by means of the output-side lines of the sensor or by means of other lines connected thereto. The frequency of the interference signals is generally considerably higher than the frequency of the useful signal. Interference pulses which are superimposed on the useful signal are fed, together with the useful signal, to the circuit arrangement for converting the output voltage of the sensor to a DC voltage. The interference signals are rectified together with the useful signal and therefore falsify the measurement result. This is particularly true for spiked interference pulses having a high amplitude.